The answer is (c); sparks will fly from the CD, as can be seen by clicking your mouse on the photograph below.
The physics behind this phenomena is quite fascinating. Any electromagnetic wave, including the microwaves used in a microwave oven, contain both electric fields and magnetic fields as they propagate. (For a quick refresher, check out a model here.)
CDs, despite their outward appearance, aren't made entirely of plastic; indeed a thin metallic layer (usually comprised of aluminum, silver or gold) is used to act as a reflective surface necessary for the laser to read the data from the disc. Aluminum, silver, and gold are--needless to say--extremely effective conductors.
When the microwaves's electric fields brush past the surface of the CD, electric potentials are formed along the conductive film layer, pointing from the higher potential to the lower potential of the wave. The electric potential difference is so great that sparks fly across the surface as currents are created between them, the sparks in turn heating the surface of the CD.
Below is a closeup of the destruction phenomena. If only you could smell
the sweet fragrance of burnt plastic through the web...
The "take home point" of this experiment is to demonstrably show that electromagnetic waves contain electric fields.
